Characterization of the Anodic Film and Corrosion Resistance of an A535 Aluminum Alloy after Intermetallics Removal by Different Etching Time

Abstract

The objective of this study was to improve the corrosion resistance of an A535 alloy by removing intermetallics on the alloy surface by alkaline etching to improve the morphologies and properties of the anodic film that was sealed with different sealants. It was found that alkaline etching for 4 min was suitable for dissolving intermetallic particles and simultaneously providing sufficient roughness for the adhesion of an oxide film to the Al matrix. The effect of alkaline etching revealed that a decrease in the intermetallic fraction from 21% to 16% after etching for 2 and 4 min, respectively, corresponded to the increase in the surface roughness, thickness, and consistency of the anodic film. It was also demonstrated that the surface morphology of the anodic films after stearic acid sealing was more uniform and compact than that after nickel fluoride sealing. The electrochemical polarization curves and salt spray test proved that the alloy etched for 4 min and sealed with stearic acid had better corrosion resistance as compared with the aluminum alloy sealed with nickel fluoride.

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“…The topology of the anodic aluminum oxide (AAO) layers depends on various factors during layer formation, including: (i) nature and concentration of the contact electrolyte [143]; (ii) applied current density or formation voltage [128,144]; (iii) composition of the to-be-anodized aluminum alloy [145][146][147][148][149] and its structure [150]; (iv) temperature [151]; (v) duration [55,152]; (vi) presence of additives [153], including Ce(IV) species [154], and of course, (vii) preliminary surface treatment [155][156][157]. Additionally, it should be mentioned that anodization at rather high voltages alters the process mechanism, converting it to plasma electrolytic oxidation (PEO).…”